Odour can be regarded as a 'pollutant' or as an indicator of the presence of pollutant. Sometimes it may alert the occupant to a potential health risk, although this need not always be reliable since some highly toxic pollutants, such as radon and carbon monoxide, are odourless. More generally, odour causes discomfort, especially in sedentary environments such as the office or home. A difficulty with odour analysis is that many odours cannot be measured by instrumentation. Evaluation, therefore, has to rely on subjective testing by 'panellists', thus making the interpretation of results difficult. A comprehensive study of odour and the control of odour by ventilation has been made by Fanger (1988).

Fanger (1988). Introduction of the olf and the decipol units to quantify air pollution perceived by humans indoors and outdoors. Energy in Buildings No12 1988.

Definitions from CEN Report CR 1752 Ventilation for buildings - Design criteria
The strength of most pollution sources indoors may be expressed as "person equivalents", i.e. the number of standard persons (olfs) required to make the air as annoying (causing as many dissatisfied) as the actual pollution source.
Perceived air quality may also be expressed in decipol (dp), where 1 dp is the air quality in a space with a pollution source strength of one olf, ventilated by 10 l/s of clean air, i.e. 1 dp = 0,1 olf/(l/s).